White-throated Treerunner

The white-throated treerunner is 15–16 cm (5.9–6.3 in) long on average, with a weight between 20–27 grams (0.71–0.95 oz). It has an appearance reminiscent of the nuthatch, with its overall look and plumage, unlike other species in the Furnariidae. Wing chord is from 76–86 mm (3.0–3.4 in), tail is 52–65 mm (2.0–2.6 in), and torso from 20–23.7 mm (0.79–0.93 in). The iris is dark brown. It has a long beak, at around 16–23.8 mm (0.63–0.94 in) with a slight upward curve. Its upper mandible is dark gray and lower mandible a whitish-pale gray. The feet are dark gray, blackish or brown. The species is easily recognized by its white throat, contrasting with its upper parts. Its face is blackish-brown and slightly darker than its head crown, which is a dull brown. The back is a paler chestnut-brown, pulling against the red rump and tail. The wing coverts are dark brown, with red or chestnut brown on the feather edges and tail end. The primaries are darker, the remiges black-brown with light edges and inner primaries marked with a short, light red wing bar. The tail is rounded, with rigid rectrices with shortened barbs ending in small spines up to 9 mm (0.35 in) long. A large white zone covers the treerunner's cheek and throat, descending to the middle of the chest. …

This species lives in central and southern Chile and western Argentina, from Santiago and Mendoza to Tierra del Fuego. It is found in the south of its distribution in the southernmost forest in the world, on Horn Island. It lives from sea level to 1,200 m of altitude, populating forests with large trees, whether dense or not, but avoiding young forests. The white-throated treerunner seeks out forests dominated by "false beech" species of the genus Nothofagus. It exploits the trunks at mid-height of trees up to the top of the canopy as a small woodpecker would. The species is sedentary, but can be erratic outside the breeding season.

Similar in behavior to nuthatches (Sitta spp.), the white-throated treerunner is a restless bird, moving in a jerky manner and changing direction rapidly. The bird may descend from trunks head first. It scours the trunks and large branches of old trees, often spiraling around the trunks, searching for small insects and their larvae in every crevice for food, sometimes tapping lightly with its bill, much like a woodpecker, or digging out larvae from under the bark with its bill. It may use its tail for support, or it may use its tail as a support for the insects. It may use their tail for support, but it also does a lot of tail-first browsing. It explores trunks quickly and spends more time foraging in smaller branches, looking for prey at the base of leaf petioles. Its diet is little known, consisting of arthropods including adults and larvae of beetles, as well as diptera. A study conducted in the province of Osorno showed that the white-throated treerunner mainly forages on trees such as Coigüe (Nothofagus dombeyi), but also Neuquén Roble (N. obliqua), Ulmo (Eucryphia cordifolia), and more generally on dead trees, even when other tree and shrub species are available. These preferences could be explained by the structure of the bark and the greater abundance of accessible insects. …

The white-throated treerunner appears in some traditional Yahgan stories as tatajurj, where it accompanies women and collects epiphytic fungi of the genus Cyttaria (katran in Yagan) from the trunks of Magellanic Beech (N. betuloides), Lenga (N. pumilio), and Ñire (N. antarctica) trees.